STUDY ON
THE JUVENILE AND TRASH EXCLUDER DEVICES (JTEDs)
IN MALAYSIA
Bundit Chok e sa n g u an,
Somboon Siriraksophon, Rosidi A li,
Suppachai Ananpongsuk and Chaichan Mahasawadee
I
t h a s b e e n re c o g n iz e d fo r s o m e tim e th a t tr a w lin g in s h a llo w c o a s ta l w a te rs h a s an adverse im pact upon the bio-diversity of the areas and m ore directly, catches the juveniles and im m ature fish seeking both for food and protection in the target w a te rs . T h e re a re s e v e ra l u n a n s w e re d re g io n a l q u e stions to w hich the solutions should be found. It has been found possible to selectively harvest single ta rg e t species, but w here there is a diversity of target s p e c ie s , a s th e r e a re in tr o p ic a l w a te r s , th e identification of the m ost suitable Bycatch R eduction D e v ic e s (B R D s ) / J u v e n ile a nd T ra s h E x c lu d e r D evices (JTED s) to perform the selective harvesting has yet to be established. It m ay well be that a variety of selective devices could be used, but certainly the experim ental approach will identify the m ost suitable designs.Today, the developm ent of fishing technology has placed m ore em phases on the design of devices having the aim of se lectively harvesting the target catch w hile at the sam e tim e reducing the level of undesirable catch in the form of juveniles, im m ature com m ercial fish and non com m ercial fish. In 1998 and 1999, SEAFD EC Training Departm ent carried out a s e rie s of e x p e rim e n ts w ith v a ry in g d e g re e s of success, in the G ulf of T hailand. T hese experim ents investigated the use of shrim p traw ls equipped with various types of Turtle Excluder Devices (TEDs). The p re lim in a ry re s u lts a nd c o n c lu s io n s fro m th e s e e x p e rim e n ts w e re re a s o n a b ly g o o d in te rm s of
c a tc h in g and re le a s e e ffic ie n c y of e c o n o m ic a lly im p o rta n t fish sp e cies. C o m p a rin g n ets w ith and w ithout TE D s proved the efficiencies of the designs.
In the year 2000, a study w as carried out in the w aters of other countries in this region, starting with the experim ents on JTE D s in Brunei D arussalam in S eptem ber 2000. In this experim ent, the design of the devices had been refined and the results indicated an im m ediate and satisfactory im provem ent. In May 2 0 0 1 , J T E D s w e re in tro d u c e d in to V ie tn a m in collaboration with RIMP of Vietnam . T he experim ent and dem onstrations w ere carried out at C at Ba Island in Hai Phong Province. M alaysia was the selected country for the im plem entation of such devices that can be beneficial as the D epartm ent of Fisheries of M alaysia, also has a project on selective fishing gear in the W est C oast of the P eninsular M alaysia.
The objectives of the activity in M alaysia are as follows; 1) to conduct experim ents and evaluations on a new type of JT E D fo r fish traw l nets, 2) To evaluate and determ ine the catching and escape level e ffic ie n c y of J T E D d e s ig n s , a nd 3) To p ro m o te s u ita b le J T E D s u n d e r th e r e s p o n s ib le fis h in g technology and practices program through training and dem onstration to M alaysian fisherm en.
This paper describes the results of the Juvenile and Trash fishes E xcluder D evice (JTED s) tested onboard a M alaysian Fishing T raw ler in cooperation
w ith th e D e p a rtm e n t of F is h e rie s , M a la y s ia . In particular, it p rovides e stim ates of C atch per Unit Effort (C PU E) of traw l fishery, catch com position in day and night tim es, distribution of length-frequencies for the capture fishes and released fishes using two different grid intervals.
MATERIALS AND METHODS
Experim ents on JTE D s attached to fish trawl n e ts w e re c o n d u c te d in c o o p e ra tio n w ith th e D epartm ent of Fisheries, M alaysia b e tw e e n 12 - 15 S eptem ber 2001 in the w aters off the coast of Kedah on the w est coast of Peninsular Malaysia. Fig
1
Shows the fishing area and local fishing traw ler em ployed for the experim ents.1. JTED Designs
T he S E A F D E C /T raining D epartm ent, having consideration to the efficiency of the escape levels fo r sm all or juvenile/trash fishes, developed a new ty p e of JT E D w hich w as m odified from the N O F I T R A O M S O A/S Sort-X. T he size of the JTED fram e w as 50 by 80 cm and com prised of three pieces. The sorting grid of 12 mm and 20 mm which covered 0.8 sq. m eters w ere placed at angle of attack of about 120°, in mouth of the codend part. In the experim ents, a co v e r net w as m o unted co ve rin g the de vice to c o lle c t th e e s c a p e d s p e c ie s . Fig 2 s h o w s th e installation and operation diagram of the JTED s.
2. Experiment and Data Collection
F is h in g e x p e rim e n ts fo r th e J T E D s w e re s c h e d u le d , and c a rrie d o u t d u rin g d a y tim e from 0 9 0 0 - 1600 hrs and in the nighttim e from 1900 - 2430 hrs. To com pare catch com position and testing the JTED for shrim p traw l operation tw o different bar spacings of 12 and 20 mm w ere tested during both day and night tim e fishing.
O ne hour traw ling with a tow ing speed of 4 to 5 knots was scheduled. The w ater depth, m easured by sounding m ethods w as betw een 20 and 28 m.
C atch data, by total w e ig h t taken from the codend and the cover net w ere recorded. For species id entification, sa m ples w ere random ly draw n from each haul. T h e y w ere sorted by species and group.
Each group or species w ere w eighed in gram s and in d iv id u a lly m e a s u re d fo r th e fo r k le n g th fo r determ ination of the length-frequency of the catch from both codends.
3. Data Analysis
All catch data from each trip w as determ ined into percentage of catch com position and catch per unit effort (CPUE in kg/hr). Because of the size the co m p o sitio n s of p o p ulation s fished, escape levels determ ined experim entally differ, thus the estim ated e s c a p e m e n t a t le n g th a re a p p lie d to le n g th fre q u e n c ie s o f c o m m e rc ia l c a tc h e s . E s tim a te s of
“overall escapem ent” w ere calculated as the w eight
or num ber of fish in the cover net divided into the total caught in the cover net and codend.
Length - fre q u e n c ie s of m ajor e c o n o m ic a lly im portant species, from both cover net and codend w e re a n a ly z e d in r e la tio n to th e p e r c e n ta g e escapem ent. Trash fishes w ere not m easured.
RESULTS AND DISCUSSION 1. CPUE and Catch Composition
T h e c a tc h p e r u n it e ffo r t (C P U E ) in th e experim ental ground are betw een 27.54 to 48.93 kg / hr / haul in daytim e and 31.69 to 35.11 kg / hr / haul in the night tim e operations. Fig 3 show s the catch composition by group ( by percentage of total w e ig h t) b e tw e e n d a y tim e a n d n ig h t tim e o p e r a tio n s . C om parison betw een day and night tim e operation found that the percentage of catch com position are clearly different. P ercentage of trash fishes, pelagic species and cephalopod group in day tim e traw ling are higher than at night. T he a m ount of catch for pelagic species, especially in day tim e is about 7 tim es higher than night tim e traw ling. In contrast, dem ersal species found at night tim e are about 3 tim es higher than in day tim e traw ling. Large shrim p like P enaeus sp. are found both in day and night tim e, how ever there are m any sm all shrim ps including M etapenaeus sp. and Tachypenaeus sp. in night tim e traw ling only.
Fig 1. Experimental ground off Alor Setar,
C om m ercial species com m only found in this experim ental ground are R a s tre llig e r brachysom a, R.
k a n a g a r ta , A tu le m a te , U p e n e u s s u lp h u re u s , S e la ro id e s leptolepis, N em ipterus sp., Priacanthus m acracanthus, large shrim p ( P enaeus sp. ), Loligo sp. and S epioteuthis sp.
2. Escape Levels
T he overall escape levels of each target group ( w ithout consideration of size ) in day tim e traw ling betw een 20 mm and 12 mm bar spacing have been com pared as shown in Fig 4. The difference in escape levels b etw een the tw o bar spacing are relatively great, not only fo r the trash fishes group but also the target group. A bout 73 % of total catch w ere released by JT E D with the 20 mm of bar spacing, and about 35 % escape levels for the 12 mm bar spacing. The trash fish group represents the highest escape levels w hich are about 87 % and 70 % fo r both 20 mm and 12 mm bar spacing of JT E D s respectively. A veraged, 63 % and 44 % of the pelagic fish and shrim p are released by a 20 mm bar spacing JTED . W hilst the 12 mm bar spacing released less than 10 % of the pelagic fish and shrim p. A bout 2-3 % of the total catch is crab including sw im m ing crab, in which 100% were found to be captured in the codend.
3. Length Frequency of Catch and Escape Levels
From the overall escape level results w ithout consideration of the size of the escaped fish, it is not possible to determ ine a suitable bar spacing for the tw o JTEDs.
Length fre q u e n c y of the catch found in the codend and cover net for different bar spacing of 20 mm and 12 mm is very useful data to decide the size of b a r s p a c in g in J T E D s . T h e re s u lts fro m the com parative study of the length frequency of som e co m m e rcia l or d o m in a n t sp e c ie s like R a s tre llig e r b ra ch yso m a , A tu le m ate, N e m ip te ru s sp., large shrim p ( P enaeus sp.), Loligo sp. and S epioteuthis sp. caught during experim ental traw ling with different bar spacings of JTED are shown in Fig 4.
T he relationship betw een the length frequency and percentage of escape levels of the R a strelliger brachysom a show that their fork length found during th is p e riod va rie d fro m 120 – 170 mm as show n in Fig 4a. The results of escape level indicate that 100
% of the R astrelliger brachysom a size larger than 120 mm will be caught by a 12 mm bar spacing JTED. In contrast, about 40% of the R a strelliger brachysom a can escape when using a 20 mm bar spaced JTED.
Fig 2. Installation of the juvenile and trash excluder devices on the fish trawl net for the experiments
Fig 3. Catch composition of day and nighttime experiments, a) daytime and b) nighttime.
T he 12 mm bar spacing JTED show good efficiency in catching m edium and larger sizes ( >120 mm ) of R a stre llig e r brachysom a both in day and night tim e traw ling.
For N em ipterus s p ., the fork length varied from 30 - 230 mm as show n in Fig 4b. T he escape results of the 12 mm bar spacing JTED show s it to be very goo d in s e le c tin g the la rg e r s ize s of N e m ip te ru s sp. ( > 110 mm ) and releasing the sm all sizes during day tim e traw ling. For night tim e traw ling with a 12 mm JTED, about 45 % of smaller sizes of fish (<110 m m ) w ere caught in the codend, this is because they live near the bottom and m ay directly pass through the codend not through the sorting grid. It show ed also the escape levels for 20 mm bar spacing.
The sam e escape results w ere found for A tule m ate (Fig 4c) .
T he dom inant species in trash fish com position w ere the ju v e n ile s of S iganus sp. All w ere in the ju ve n ile stage size sm aller than 70 mm M ore than 70% of these ju veniles w ere released through the sorting grid.
Many squid and cuttlefish were found especially in day tim e trawling. The squid found in this area were from 3 0 - 140 mm m antle length. A bout 80 % of the total catch of squid escaped through the 20 mm bar spacing JT E D and about 50 % could escape through the 12 mm JTED in day tim e traw ling. It is probable th a t the squid m ove vertically to the upper layer at night tim e, therefore, less squid w ere caught during the day tim e experim ents.
For cuttlefish the escape levels related to the size of the cuttlefish, w hich varied from 50 - 290 mm m antle length. Using the 20 mm JTED could release
about 65 % of the 5 0 - 130 mm cuttlefish. For the 12 mm JTED , only cuttlefish of less than 100 mm could escape, however, they w ere very few in num ber.
Large shrim p like P enaeus m e rguiensis and P. sem isulcatus varied betw een 100 - 200 mm Fig 4d show s the escape results of shrim p for the 12 mm bar spaced JTED , there is no sig nificant difference in the catch of large shrim p betw een day and night time. It indicates that only about 5% of the total shrim p could escape from the so rting grid of 12 mm bar spacing and about 95% of shrim p (>100 mm) w ere caught in the codend. In the case of the 20 mm bar spaced JTED, som e large shrim p (up to 190 mm long) c o u ld e s c a p e . T h is s h o w s th e e ffic ie n c y in size selection of the 12 mm spaced sorting grid.
CONCLUSION
T h e Im p le m e n ta tio n a n d in tr o d u c tio n of selective devices is very urgent in the S outhea st A sia C ountries because of the over-fishing of the m arine resources of both dem ersal and p e la g ic fish. T he JTED is one of the size selection devices that can be used to release sm all sizes of fish and catch on ly the larger sizes. T he principal of using this device is that the target species or large size of fish, shrim p or squid / cuttlefish should be retained in the codend and the s m a ll/ ju v e n ile s h o u ld be r e le a s e d . F ro m th e experim ents in this study, the 12 mm bar spacing JTED m ay be a suitable device to release the juvenile and sm all fishes including trash fish fo r sustainable fishing. D etailed studied m ust to be carried out to confirm this conjecture.
O th e r fa c to r s lik e e a s y in s t a lla t io n a n d operation for fisherm en m ust also be considered. A design review and im provem ent of the devices to fulfil these factors is essential.
Fig 4. Length frequencies of some commercial or dominant species like Rastrelliger brachysoma (a) Nemipterus sp. (b), Atule mate (c), and large shrimp (Penaeus sp.) (d) which were caught from experimental trawling with different bar spacings of the JTED
ACKNOWLEDGEMENTS
W e should like to express sincere thanks to the G o ve rn m e n t of Japan through the T rust Fund Project for supporting and m aking this study possible.
O ur gratitude is also to those w ho contributed to the success of this study.
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